Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$95.75	10.596%	$105.8957	$105.90	$105.90	$105.90
Purchase #2	$51.74	13.786%	$58.8729	$58.87	$58.85	$58.90
Purchase #3	$220.95	4.303%	$230.4575	$230.46	$230.45	$230.50
Purchase #4	$48.39	9.716%	$53.0916	$53.09	$53.10	$53.10
Purchase #5	$157.97	11.421%	$176.0118	$176.01	$176.00	$176.00
Purchase #6	$173.42	10.403%	$191.4609	$191.46	$191.45	$191.50
Purchase #7	$50.78	7.571%	$54.6246	$54.62	$54.60	$54.60
7 purchase totals =	$799.00		$870.4150	$870.41	$870.35	$870.50